Respirometric methods provide direct measurements of the oxygen consumed by microorganisms from an air or oxygen-enriched environment in a closed vessel under conditions of constant temperature and agitation. Carbon dioxide produced metabolically by the bacteria is chemically bound by the potassium hydroxide solution contained in the seal cup in the bottle.
The result is a pressure drop in the system, which is directly proportional to the BOD value and is measured by the Lovibond® BOD sensor. The BOD level is then displayed directly in mg/l.
Measuring ranges and sample volumes
The BOD level of a sample depends on the quantity of organic matter present, which can vary considerably.
The Lovibond® BOD measuring system OxiDirect is therefore calibrated for the various sample volumes and the corresponding measuring ranges listed in the table below.
• Waste Water
• Determination of Biological activity
• Waste Water Treatment Plants
• analytical Laboratories
• science & Research
• Maintenance-free and non-wearing
• Regular change in stirring speed
• automatic centering of stirring rods
• No mechanical components
in the stirring system
Evaluation of measurements
If the measuring period is set at 24 hours, the Lovibond® OxiDirect BOD measuring system records a measurement once every hour. With a measuring period of 48 hours, the unit measures and stores a BOD value once every 2 hours. If the measuring period is between 3 and 28 days, one value is measured and stored each day.
Current values and stored values may be called up at any time. The table/graph below illustrates an example of BOD5 evaluation. The development of BOD over a period of 5 days is easily seen.
Automatic Start Function
Variations in sample temperature prior to testing result in pressure variations within the measuring system during the temperature equalisation period in the thermostatically controlled cabinet (if BOD measurement is to take place at 20°C, for example).
Such variations would normally cause errors during manometric measurement.
The complete OxiDirect measuring system
In addition to the BOD unit for measurement and storage of BOD levels, the Lovibond® OxiDirect BOD measuring system includes sample bottles, measuring sensors, non-wearing inductive stirring system, overflow measuring flasks for metering of sample volumes, nitrification inhibitor and potassium hydroxide as an absorbent.
Test set for OxiDirect
We also supply a test set to check for correct operation of the Lovibond® OxiDirect BOD meter. The set contains 8 BOD CM1 test tablets that cause a defined oxygen consumption.
Temperature equalisation during BOD measurement
Temperature equalisation is essential prior to biological testing, as temperature has a major effect on biological activity. BOD measurements, for example, are always performed in a thermostatically controlled cabinet at a temperature of 20°C.
Meas. Principle : Manometric; mercury-free; electronic pressure sensor
Ranges [mg/l O2] : 0 – 40, 0 -80, 0 – 200,
0 – 400, 0 – 800,
0 – 2000, 0 – 4000 mg/l
Accuracy* : 0.5 % full scale at 20°C
Applications : BOD5, BOD7, OECD 301 F …
Result display : BOD [mg/l]; 4 – digits; 7 – segment LED
Measurement parameter display : BOD-range, volume, duration, time of measurement
Measurement period : User-selectable, between period 1 and 28 days